Spot-type disc brake with resetting means

ABSTRACT

In a spot-type disc brake for motor vehicles a floating caliper is guided displaceably on a brake support by means of sliding pins (26). Inner and outer brake pads are likewise displaceably mounted parallel to the sliding pins with respect to the brake support. On at least one of the sliding pins a resetting means (50) with a spring (52) is provided which is arranged around the sliding pin as part of a frictionally locking connection between the sliding pin and a bore guiding said pin. The bore (24) comprises at the end from which the sliding pin is inserted into said bore a widening (54) into which the spring (52) is installed with axial bias. The spring or a member cooperating therewith is in engagement with an outer surface of the sliding pin.

The invention relates to a spot-type disc brake, in particular for motorvehicles, comprising

a floating caliper which is displaceably guided on a brake support bymeans of sliding pins,

an inner and an outer brake pad which are displaceable parallel to thesliding pins with respect to the brake support,

an actuator with which the inner brake pad is operable directly and theouter brake pad by displacement of the floating caliper and

a resetting means on at least one of the sliding pins including a springwhich is arranged around the sliding pin as part of a frictionalconnection between said pin and a bore guiding said pin and isresiliently yieldable to a limited extent in the axial direction.

In a known disc brake of this type (DE-PS 2,211,429) the sliding pinsare detachably secured on the floating caliper and each displaceablyguided in a bore of the brake support. In disc brakes of the typeaccording to the preamble it is however also fundamentally possible forthe sliding pins to be mounted on the brake support and each guided in abore of the floating caliper. In both cases, on actuation of the brakethe floating caliper is displaceable in such a manner that the outerbrake pad, with respect to the associated vehicle, is pressed by thefloating caliper against a brake disc when the actuator presses theinner brake pad directly against the brake disc. After actuation of thebrake it is necessary for the two brake pads to be moved away from thebrake disc by a predetermined distance, the so called release clearance.The release clearance should on the one hand be large enough to preventunder all circumstances, for example when the brake disc is deformed byheat or when travelling round a curve, the brake pads rubbing on thebrake discs. On the other hand, the release clearance should be as smallas possible to avoid making the pedal travel required on the nextactuation of the brake unnecessarily large.

The release clearance of the brake pad operated directly by theactuator, the inner pad with respect to the vehicle, is generallygoverned by an actuating piston which is associated therewith and whichis reset by a piston seal resilient in the axial direction. However, indisc brakes according to the preamble the resetting means mentioned atthe beginning on at least one of the sliding pins is responsible formaintaining a predetermined release clearance of the outer brake padactuable by displacement of the floating caliper.

In the known disc brake described the sliding pins each comprise attheir end received in the associated bore an annular groove in which aspring element in the form of a resilient ring is accommodated in such amanner that its outer peripheral face bears in frictionally lockingmanner on the cylindrical wall of the bore. The spring element opposes adisplacement in the axial direction with a frictional resistance suchthat its cross-section deforms resiliently under a normal brakeactuation and thereby builds up an axial resetting force which sufficesto return the floating caliper to its original position after the brakeactuation. The frictional resistance between spring element and bore ishowever overcome on actuation of the brake when the release clearancedue to wear of the brake pad has exceeded a predetermined amount; inthis case the spring element in the bore is displaced into a newposition from whence the spring element effects the resetting of thefloating caliper after release of the brake.

With the known arrangement it has proved to be difficult and expensiveto maintain with adequately narrow tolerances the dimensions, decisivefor the magnitude of the frictional resistance, of the annular springelement, the sliding pin and the associated bore. The frictionalresistance after overcoming which the spring element can be moved in thebore is thus subject to considerable fluctuations. If the frictionalresistance is too small the spring element is unable to build up aresilient resetting force adequate for the return of the floatingcaliper; if however the frictional resistance is too large the brake paddisplaceable by the floating caliper on actuation of the brake ispressed against the brake disc with a smaller force than the brake paddisplaceable directly by the actuator.

The invention is therefore based on the problem of further developing adisc brake of the type described at the beginning in such a manner thatin spite of inevitable production tolerances of its componentsresponsible for resetting the floating caliper a predetermined resettingforce can be maintained within narrow limits.

The problem is solved according to the invention in that the borecomprises at an end from which the associated sliding pin is insertedinto said bore a widening into which the spring is installed with axialbias and that the sliding pin comprises in its region cooperating withthe spring a cylindrical outer surface.

As a result for a given diameter of the sliding pin an annular spring oflarger diameter than in the known brake according to the preamble can beinstalled and the axial bias of the spring can be fixed by simple steps,possibly even after installation of the sliding pin, in such a mannerthat in spite of inevitable diameter tolerances of the sliding pin andof the spring itself a predetermined frictional resistance to movementsof the floating caliper is exactly achieved and thus also apredetermined resilient resetting force acting on the floating caliper.

These advantages of the arrangement according to the invention areindependent of whether the spring is a ring of rubber or resilientplastic as known from cited DE-PS 2,211,429 or for example a helicalspring which with a narrow convolution encloses in frictionally lockingmanner the sliding pin and with a wide convolution bears on thecomponent on which the bore and the widening thereof are formed.

A resetting means having such a helical spring is provided in DE-GM1,977,258 on the piston of a pneumatic or hydraulic brake actuator. Inthe latter the piston is arranged within a cylinder which is open at oneend and is provided with an axial bore into which a pin mounted at theclosed end of the cylinder projects. The bore has a widening in whichthe helical spring is arranged. The helical spring has at its two endsconvolutions of large diameter which do not contact the pin and bear ona shoulder of the piston or on a disc mounted on the piston; betweensaid ends the helical spring has convolutions of smaller diameter whichsurround the pin in frictionally locking manner. With this knownarrangement only the actuating piston can be reset and adjusted but notthe floating caliper of a disc brake. The pin mounted on the cylinderhas no guide function and is only part of the resetting means whichtherefore represents a considerable constructional expenditure.

In contrast thereto, in the subject of the invention at least one of thesliding pins present in any case for guiding the floating caliper isused simultaneously as part of the resetting means without thereforehaving to be different in any feature at all from a sliding pin which isused only for guiding the floating caliper and does not cooperate with aresetting means.

In a preferred embodiment of the invention the spring is clamped betweena shoulder defining the widening of the bore and a rigid ring crimped atthe edge of the widening.

In a preferred further development of the invention the spring isdivided into two parts and comprises a first spring element which isbiased in axial direction and a second spring element which is biased inradial direction. With such a dividing of the spring into two theradially and axially acting biases can be adapted to each other insimple manner. The bias in the axial direction is less than the bias inthe radial direction.

In a preferred embodiment of the invention as first spring element ahelical spring and a second spring element a slit ring are provided. Insuch an embodiment of the two-part spring the sliding pin can becentered in simple manner with respect to the bore when the widening ofthe bore is conically formed and the slit ring tapers conicallycorrespondingly on one side. With such an arrangement both the resettingforce for the resetting means can be kept in narrow limits and an exactguiding of the sliding pins is ensured so that undesirable rattling ofthe parts against each other is avoided.

In a particularly preferred embodiment of the invention the secondspring element is pressed by the first spring element in the radialdirection. In this case the second spring element itself need notgenerate any bias in the radial direction but instead is pressed by thefirst spring element against the sliding pin.

It is also possible to press the second spring element in the axialdirection by the first spring element and in a preferred embodiment thesecond spring element slides on a conical face in such a manner that aradial inwardly directed force component arises which presses the secondspring element against the sliding pin.

The spring or spring elements may be made from rubber or resilientplastic. Examples of embodiment of the invention will be explained withfurther details hereinafter with the aid of schematic drawings, wherein:

FIG. 1 is a plan view of a spot-type disc brake,

FIG. 2 is the axial section II--II of FIG. 1,

FIG. 3 is the side view of the brake shown partially as radial sectionIII--III of FIG. 1,

FIG. 4 is an enlarged partial section IV--IV of FIG. 1,

FIG. 5 shows a detail corresponding to FIG. 4 of another example ofembodiment of the invention, and

FIGS. 6 to 10 show further examples of embodiment of spot-type discbrakes according to the invention.

The spot-type disc brake illustrated is associated with a brake disc 10mounted on a wheel hub 12. In FIG. 2 part of an associated wheel rim 14is also indicated. A brake support 20 having two arms 22 is secured to astationary member 16 by means of a pair of screws 18. The arms 22 extendparallel to the axis of the brake disc 10 beyond the outer edge thereofand each have an axis-parallel bore 24. A sliding pin 26 is displaceablyguided in each of the bores 24.

A floating caliper 30 is mounted in each case with a screw 28 on the twosliding pins 26 and also engages beyond the radially outer edge of thebrake disc 10. At the axially inner end of the floating caliper 30 withrespect to the associated vehicle a hydraulic actuator 32 is mountedwhich has a piston 34. The piston is surrounded by a resilient pistonring 36 which acts as seal and at the same time is constructed asresetting means for the piston. Axially opposite the piston 34 on theother side of the brake disc 10 a pair of legs 38 is formed on thefloating caliper 30. Associated with the piston 34 is an inner brake pad40 operable directly thereby. In corresponding manner an outer brake pad42 is associated with the pair of legs 38 and is to be actuated by theactuator 32 indirectly by displacement of the floating caliper 30.

Each of the two brake pads 40 and 42 comprises a support plate 44 whichis displaceably guided in a cutout 46 of the brake support 20 parallelto the axis of the brake disc 10 and is supported against forces in theperipheral direction and in the radial direction of the brake disc 10.Mounted on the support plate 44 of each of the two brake pads 40 and 42is a holding-down spring 48 which bears radially outwardly on thefloating caliper 30 and thereby biases the latter radially outwardlywhile it biases the brake pads radially inwardly and thereby preventsall these displaceable members from rattling on vibrations.

Associated with the floating caliper 30 is a resetting means 50 whichtends after each actuation whenever the actuator 32 is pressureless toreturn said caliper to an inoperative position in which the outer brakepad 42 has a predetermined distance from the face of the brake disc 10facing said caliper, said distance being referred to as brake releaseclearance, while the piston ring 36 ensures a corresponding releaseclearance for the inner brake pad 40.

Belonging to the resetting means 50 are two springs 52 each arrangedround one of the sliding pins 26 in a respective widening 54 at the openend of the associated bore 24. Each of the widenings is defined on theone hand by a radial shoulder 56 of the associated bore 24 and on theother by a rigid ring 58 mounted by crimping 60 at the open end of therespective widening 54. The distance between the shoulder 56 and thering 58 is so dimensioned that the spring 52 is kept under axial bias.

Each of the resetting means 50 is surrounded by a resilient packingsleeve 62 which sealingly connects the associated arm 22 to theassociated sliding pin 26. Each of the sliding pins 26 has a hexagonalhead 64 which is disposed outside the associated packing sleeve 62 andcan be engaged with an open-ended spanner to prevent the respectivesliding pin from turning when the floating caliper 30 is to be removedby releasing the associated screw 28, for example for replacing thebrake pads 40 and 42.

In accordance with FIG. 4 each of the springs 52 is formed by a helicalspring which has a narrow and a wide convolution. The narrow convolutionencloses a cylindrical region 66 of the sliding pin 26 with radial biasand normally bears on the shoulder 56. The wide convolution of thespring 52 has a radial spacing from the cylindrical region 66 and bearson the ring 58.

On actuation of the brake the floating caliper 30 is moved inwardly, tothe left in FIG. 4; each of the two sliding pins 26 entrains the narrowconvolution of the associated spring 52 so that an axial resetting forceis built up in the spring. These resetting forces ensure that after therelease of the brake the floating caliper 30 is returned to its originalposition.

If however the movement of the floating caliper 30 occurring onactuation of the brake and thus also of the two sliding pins 26 exceedsthe predetermined amount by which the narrow convolution of each of thetwo springs 52 is movable within the associated widening 54, a slidingrelative motion then takes place between the sliding pins and thesprings and the narrow winding thereof assumes a new starting positionon the cylindrical region 66 of the associated sliding pin 26, fromwhence the floating caliper 30 is reset on release of the brake.

In the embodiment illustrated in FIG. 5 a ring of rubber or resilientplastic 52 acts like the spring 52 illustrated in FIG. 4 but comparedwith the latter has the additional advantage that the spring energystored therein with the brake actuated is not lost even under strongvibrations and is thus available in every case with greater certaintyfor resetting the floating caliper 30.

In the embodiment illustrated in FIG. 6 a spring corresponding to thespring 52 of FIG. 4 is divided into two parts and comprises a firsthelical spring element 52a and a second spring element 52b constructedas slit ring. In the installed state the second spring element 52bformed as slit ring is radially biased while the first helically formedspring element 52a is biased in the axial direction. The axial bias issubstantially less than the radial bias. 2 kp has proved to be asuitable value for the axial bias while the radial bias is dimensionedso that a frictional force is generated between the slit ring and thesliding pin 26 which lies between 5 and 10 kp, i.e. the force which isnecessary to move the slit ring on the sliding pin lies in said range.

In accordance with FIG. 6 the slit ring 52b is provided with a conicalface 70 which is complementary to a conical face formed in the widening54 of the bore 24. Consequently, the sliding pin 26 and the membercarried thereby are exactly aligned and undesired rattling prevented.

When the brake is actuated the slit ring 52b is moved the distance "x ",about 0.2 to 0.6 mm, with the sliding pin 26. The distance "x"corresponds to the release clearance. If the movement of the sliding pinexceeds the distance "x" the slit ring 52b meets the rigid ring 58 andis displaced on the sliding pin 26 corresponding to the wear of thebrake linings so that the release clearance remains constant.

FIGS. 7 to 10 show further examples of embodiment. Parts correspondingto the examples of embodiment described so far are provided with thesame reference numerals.

In the example of embodiment according to FIG. 7 the second springelement 52c is made cup-shaped and surrounds the first spring element52d. The first spring element 52d bears in FIG. 7 on the left on thering 58 and on the right presses the spring element 52c against theconical face 70 so that the second spring element 52c due to the slidingdown on the conical face is given an inwardly directed force componentand is thus pressed against the sliding pin 26. The reset distances aredenoted by the reference numerals r₁ and r₂.

In the example of embodiment according to FIG. 8 the second springelement 52e is a slit ring of metal, for example brass. The diameter ofthe slit ring is somewhat smaller than the diameter of the sliding pin26 so that the second spring element 52e presses with a desired biasagainst the sliding pin 26. The frictional force between the secondspring element 52e and the sliding pin is set to 5 to 10 kp. Accordingto FIG. 8 the distance a between the rigid ring 58 and the spring stopat the second spring element 52e is less than the distance from therigid ring 58 to the last spring convolution so that the first springelement 52f is not stressed by blocking.

In the example of embodiment according to FIG. 9 the second springelement 52g is made conical and formed as slit ring. Suitable materialfor the second spring element 52g is steel, cast-iron, brass or plastic.The first spring element 52h engages with its convolution lying furthestto the right in the Figure in a recess round the second spring element52g and holds the latter together. This generates part of the desiredfrictional resistance between the second spring element 52g and thesliding pin 26. At the same time the first spring element 52h presses inthe axial direction against the second spring element 52g so that thelatter slides down the conical face, thereby also causing a radiallyinwardly directed force component to act on the second spring element52g.

The embodiment according to FIG. 10 provides a three-part springarrangement. In addition to the first and second spring elements 52i,52j an intermediate piece 52k is provided. The first spring element 52iis made as in the example of embodiment of FIG. 7 as a helical springacting in the axial direction. The second spring element 52j is formedas O-ring and bears on a conical face 70. The intermediate piece 52ktransmits the force of the first spring element 52i acting in the axialdirection to the O-ring 52j so that at the conical face 70 a radiallyinwardly directed force component arises which presses the O-ringagainst the sliding pin 26 and there generates the desired friction.

In all the embodiments, a slight play between the sliding pin 26 and thebore receiving said pin in the arms 22 of the brake support 20 ispresent due to tolerances in the manufacture. By the fixing provided inthe described embodiments the sliding pin 26 is centered in the bore andtilting of the sliding pin positively prevented. This ensures easymoving of the brake.

We claim:
 1. Spot-type disc brake comprisinga floating caliper memberwhich is displaceably guided on a brake support member by means ofsliding pins, an inner and an outer brake pad which are displaceableparallel to the sliding pins with respect to the brake support member,an actuator with which the inner brake pad is operable directly and theouter brake pad by displacement of the floating caliper, and a resettingmeans on at least one of the sliding pins carried by one of said membersincluding a spring which is arranged around the sliding pin as part of africtional connection between said pin and a bore in the other of saidmembers guiding said pin and is resiliently yieldable to a limitedextent in an axial direction, the bore comprising at one end, from whichthe associated sliding pin is inserted into said bore, a widening inwhich the spring is installed, wherein the spring comprises a first anda second spring element, the first spring element is a coil spring andbiased in axial direction, one end of said first spring element issupported by a rigid ring which is attached to an edge of the widening,and an other end of said first spring element is supported at the secondspring element, said first spring element reacting against said secondspring element to reset said floating caliper to its original positionupon release of the brake, the second spring element comprises a conicalsurface which is urged into engagement with a complementary conicalsurface of said widening of said bore by the axial bias of said firstspring element, characterized in that said second spring element is aslit ring which is radially biased into engagement with said pin andsaid radial bias is substantially greater than said axial bias producedby said first spring element, and that said second spring element andsaid first spring element act together to retain said pin substantiallyrattle free within said bore.
 2. A spot-type disc brake as claimed inclaim 1, wherein at least a portion of said radial bias is produced bythe radial component of the axial force from the first spring elementacting on the second spring element in the direction of the conicalsurface formed in the widening of the bore.
 3. Spot-type disc brakecomprisinga floating caliper member which is displaceably guided on abrake support member by means of sliding pins, an inner and an outerbrake pad which are displaceable parallel to the sliding pins withrespect to the brake support member, an actuator with which the innerbrake pad is operable directly and the outer brake pad by displacementof the floating caliper, and a resetting means on at least one of thesliding pins carried by one of said members including a spring which isarranged around the sliding pin as part of a frictional connectionbetween said pin and a bore in the other of said members guiding saidpin and is resiliently yieldable to a limited extent in an axialdirection, the bore comprising at one end, from which the associatedsliding pin is inserted into said bore, a widening in which the springis installed, wherein the spring comprises a first and a second springelement, the first spring element is a coil spring and biased in anaxial direction, one end of said first spring element is supported by arigid ring which is attached to an edge of the widening, and an otherend of said first spring is supported at the second spring element, saidfirst spring element reacting against said second spring element toreset said floating caliper to its original position upon release of thebrake, the second spring element comprises a conical surface and isclamped by the axial bias of the first spring element between acomplementary conical surface of said widening of said bore and saidpin, characterized in that said second spring element is a slit ring andradially biased, the radial bias being substantially stronger than saidaxial bias, and that said second spring element comprises a step whichis embraced by a portion of the windings of said first spring element.4. Spot-type disc brake comprisinga floating caliper member which isdisplaceably guided on a brake support member by means of sliding pins,an inner and an outer brake pad which are displaceable parallel to thesliding pins with respect to the brake support member, an actuator withwhich the inner brake pad is operable directly and the outer brake padby displacement of the floating caliper, and a resetting means on atleast one of the sliding pins carried by one of said members including aspring which is arranged around the sliding pin as part of a frictionalconnection between said pin and a bore in the other of said membersguiding said pin and is resiliently yieldable to a limited extent in anaxial direction, the bore comprising at one end, from which theassociated sliding pin is inserted into said bore, a widening in whichthe spring is installed, wherein the spring comprises a first and asecond spring element, the first spring element is a coil spring andbiased in an axial direction, one end of said first spring element issupported by a rigid ring which is attached to an edge of the widening,and an other end of said first spring is supported at the second springelement, said first spring element reacting against said second springelement to reset said floating caliper to its original position uponrelease of the brake, the second spring element comprises a conicalsurface and is clamped by the axial bias of the first spring elementbetween a complementary conical surface of said widening of said boreand said pin, characterized in that said second spring element iscup-shaped and surrounds the first spring element.
 5. Spot-type discbrake according to claim 1, characterized in that the second springelement is pressed by the first spring element in the radial direction.6. Spot-type disc brake according to claims 1 or 2, characterized inthat the second spring element comprises a resilient rubber-likematerial.